FIELD ISOLATES OF TRANSMISSIBLE GASTROENTERITIS VIRUS DIFFER AT THE MOLECULAR-LEVEL FROM THE MILLER AND PURDUE VIRULENT AND ATTENUATED STRAINS AND FROM PORCINE RESPIRATORY CORONAVIRUSES

The diversity in selected regions of the transmissible gastroenteritis virus (TGEV) and porcine respiratory coronavirus (PRCV) genomes was a nalyzed among known TGEV and PRCV strains and field isolates. The N-te rminal half of the spike (S) glycoprotein gene and open reading frames (ORF) 3, 3-1 and 4 were amplified by reverse transcriptase reaction a nd polymerase chain reaction (RT/PCR), and analyzed using restriction fragment length polymorphism (RFLP) patterns of the amplified DNA. Ref erence TGEV strains (Miller and Purdue) and a PRCV strain (ISU-1), and TGEV and PRCV field isolates were analyzed. Based on the size of the ORF 3, 3-1 and 4 RT/PCR products, TGEV and PRCV strains could be quick ly and easily differentiated into three groups designated TGEV Miller, Purdue types and PRCV. By RFLP analysis of the N-terminal region of t he S glycoprotein gene and ORFs 3, 3-1 and 4, TGEV and PRCV strains we re differentiated into five groups using the restriction enzyme Sau3AI . Sequence analysis of a PCR product in the ORFs 3, 3-1 and 4 from vir ulent and attenuated Miller strains demonstrated additional difference s in that region which have been correlated with a change in virulence of TGEV isolates.